Contactless electronic keyboard array

ABSTRACT

An electronic keyboard system includes a key structure comprising primary and secondary coils coupled together by a magnetic shaft when moved to produce primary signals from a pulse train in the secondary. A magnetic shield between the coils produces a sharp transistor between no-signal and signal condition in the secondary winding as the shaft is moved past a critical position. Electronic circuitry provides for converting the pulse train into a single output pulse for each key depression, by use of a single Schmidt trigger circuit coupled into an encoding matrix to produce a coded signal for each separate key.

United States Patent 9 [72] inventor John Paul JonesJr. 3,172,939 3/1965 Campbell 84/1 .01 Wayne, Pa. 3,221,120 11/1965 Mooney 84/1 .15 [21] Appl. No. 852,590 3,249,199 5/1966 Jones .1 197/19 [22] Filed Aug. 25, 1969 3,363,737 1/1968 Wada 197/98 [45] Patented July 20, 1-971 Primary Examiner-Milton 0. Hirshfield Assign Niven Assistant Examiner-R. Skudy Attorney-Laurence R. Brown [54] CONTAC'I'LESS ELECTRONIC KEYBOARD ARRAY ABSTRACT: An electronic keyboard s stem includes a key 5 Claims 5 Draw F y mg structure com d d 'l 1 d prising pnmary an secon ary CO1 s coup e [52] US. Cl. 84/ 1.1, together by a magnetic shaft when moved to produce primary g 8 l .15 signals from a pulse train in the secondary. A magnetic shield [S 1] InLCl G0lh 3/00 between the coils produces a sharp transistor between no- [50] Field of Search 84/l.01, i al and ignal condition in the secondary winding as the 98 shaft is moved past a critical position. Electronic circuitry provides for converting the pulse train into a single output pulse [56] Rdemm for each key depression, by use of a single Schmidt trigger cir- UNITED STATES PATENTS cuit coupled into an encoding matrix to produce a coded 1,183,685 5/1916 Sinclair 84/1. 1 signal for each separate key.

CONTACTLESS ELECTRONIC KEYBOARD ARRAY This invention relates. to electronic keyboard systems, and more particularly to keyboard arrays with contactless keys.

Electronic keys in the prior art have primarily incorporated mechanical switching contacts of various types. All of these have suffered from the general problem of switch bounce which in electronic systems tends to introduce false signals and errors. Also some mechanical contacts have limited life spans. Critical applications of electronic keyboard system in military, traffic control or digital systems require higher performance standards that will not tolerate mechanical switch bouncedeterioration or other associated problems. Wherever switches are subjected to vibrations the mechanical contacts become even less reliable. Also environmental conditions such as humidity'or temperature changes can cause variations in contact performance. For these reasons switchless contacts involving photoelectric devices and the like may fail even if their added cost is permissible.

It is therefore a general object of this invention to provide improved contactless electronic keyboard arrays.

Another object of the invention is to provide a rugged and inexpensive keyboard array which provides a high degree of uniformity and which can be made simply with noncritical techniques.

' Therefore in accordance with the invention a keyboard switch employing magnetic coupling techniques such as those defined in my US. Pat. No. 3,249,l99 are employed in a system providing from a train of pulses coupled through the actuation of the key to electronic utilization means a single defined output pulse of known characteristic for each key depression. The key design is an improved design providing for a sharp signal transition as the key shaft is moved past a critical position. I

The equipment afforded by this invention is defined in more detail with'reference to the accompanying drawing, in which:

FIG. 1 is a section view sketch of a magnetically coupled key in its rest position,

FIG. 2 is a section view sketch of a magnetically coupled key in its operated position,

FIG. 3 is an elevation view in cross section of a key assembly constructed in accordance with this invention, I

FIG. 4 is a schematic diagram of a keyboard system operable to produce a single pulse of known characteristics from each key stroke, and

FIG. 5 is a waveform diagram illustrating operation of the system of FIG. 4.

In FIG. 1, the electronic key device comprises a finger rest key button coupled to a longitudinally oriented shank or shaft 11 of magnetic material of low reluctance such as soft iron extending axially part way into the core of a pair of coils l4, l5 wound about the axis of shank 11. In accordance with this invention a magnetic shield washer 16 of low reluctance material separates the primary coil 14 at which pulse train 17 is continuously coupled from the secondary coil 15 having output terminals l8, 19. As seen from FIG. 1 this washer l6 7 works as a flux gate to confine the magnetic field lines within the region of primary coil 14 when the key is in its rest position shown with the shank ll terminating at a position 21 on the primary coil side of the magnetic washer 16.

This construction provides a sharp transition characteristic as the shank 11 is moved through a critical position at magnetic washer 16 so that input pulse train 17 couples into the secondary winding 15 to provide a corresponding output pulse train 22 as the modified flux lines 20' cut through both the primary l4 and secondary 15 from the modified end position 21' of the magnetic shank 11.

As may be seen in FIG. 3, the key is normally biased into its rest position by means such as spring 25 about shank II. The

shank 11 may be provided with an extension 26 of nonmagnetic material such as nylon having high reluctance which will adapt it to operate a standard keyboard in the manner described in the aforesaid patent. This shank extension 26 may have a keyed extension 27 mating with a keyed slot in the base portion 28 which extends part way through a cylindrical shaft 29 to define the upper rest position of key button 10, and thus confine it from rotation. The tapered construction of base member 28 adapts to a standard keyboard panel slant. Pins 24 extend through base member 28 to provide electrical access terminal connections for the coils l4 and 15.

To enhance the magnetic coupling characteristic of the key structure a hood 30 of low reluctance magnetic material en- 'velops both coils and extends to the vicinity of shank II at the top to provide a return path for flux passing through secondary coil I5. I

This key structure in FIG. 4 is coupled to a system for utilizing the pulse train passed through secondary winding 15 into the transistor amplifier 31. An oscillator 32 may provide the pulse train I7 of pulses having a duration of microseconds and a duty cycle of I to 10, for example, of enough magnitude to produce output pulses 22 from the secondary winding 15 of enough amplitude to overcome a bias voltage of 0.5 volts for example at the emitter terminal 33 of transistor 31. The oscillator 32 may be connected by a bus connector 34 to a plurality of separate keys in a keyboard array (not shown). Each separate key has an individual output lead 35 which is coupled to a selected set of outputlines 37 by a corresponding set of diodes 36. Each output line 37 may include an amplifier 38 and a gate 39 so that the output code of any key is uniquely defined by a combination of signals at oneor more output leads 40.

To assure that a single output pulse is defined for each key depression several precautions are taken in the circuit of FIG. 4. An envelope of pulses 17, for example 35 microsecond pulses at a 3 kilocycle repetition rate, is passed from one or more of lines 37 through OR diodes 4lint o lead 42. The capacitor 43 accumulates these pulses with the help of an integration circuit 44 to produce a pulse waveform 51 built up from the successive 3 kc. pulses as shown in FIG. 5.

Flip-flop circuit 60 is operated as a Schmidt trigger circuit to fire once from input waveform 51 to produce output pulse 59' which is differentiated from pulse 59 (FIG. 5) at capacitor 68. Pulse 59 is amplified through inverter 69 to produce at lead a pulse of sufficient length to open gates 39 for passing a single pulse 17 from oscillator 32 through each of the leads 40 connected by diodes 36 to the transistor output lead 36, provided key 10 is depressed to gate pulses 22 into the transistor circuit 31.

The firing and reset points of flip-flop 60 are set up by the adjustable input resistors 64 and 65 respectively to drive the flip-flop input 61 directly and input 62 through inverting'amplifier 63. In practice the adjustable resistor 65 is set to make the inverter 63 conduct to ground at the threshold level 54 of input waveform 51 (FIG. 5 This removes the reset voltage at flip-flop terminal 62. As the waveform continues to build up at lead 42, and is integrated, the'conduction point of the flip-flop at lead 61 is reachedat a level selected by setting resistor 64. When the flip-flop 60 fires the gate pulse 59' will be produced to gate a single following pulse 17 of the pulse train passed while the key) is depressed.

Only when key 10 is released does the pulse train fall off in amplitude as the shank ll extremity nears the critical point at washer 16, to thereby'cause a steep falloff slope 53 in amplitude of the input pulses at lead 42. When the amplitude falls below threshold level 54 the inverter 63 will fire flip-flop 60 at lead 62 to terminate pulse 59 in a reset operation for the Schmidt trigger circuit.

This described mode of operation is important to avoid any stuttering or double firing of a key such as provided when it is in the critical region with the extremity of shank 11 near washer 16. Also it affords synchronization of timing with oscillator 32 for output pulses at leads 40. Of particular importance is the hysteresis portion 55 of the waveform 51 as employed in this carrier detection operation to assure that the key 10 can pass through the critical region without firing more than once.

in this respect transistor 31 plays a role in detecting and amplifying the pulsetrain and producing the firing threshold. A silicon transistor may be employed having an input conduction level between base and emitter of about 0.75 volts. This means that shankll must pass the gating washer l6 and provide enough flux in coil N to build up 0.75 volts before output pulses are afforded at transistor output lead 35. This affords the magnetic material in theshank through said magnetic plate to enter the second coil.

noise immunity to prevent spurious triggering possibilities,

and operates the transistor amplifier as a threshold comparator greatly sharpening the transition from no pulse to full pulse amplitude in response to the depression of the key.

What I claim is:

1. Structure operable in an electronic keyboard comprising in combination, an electronic key device manually actuable from a key button having a longitudinally oriented shank coupled to the key button and movable axially over a confined span of longitudinal movement, magnetic material of low reluctance in at least a portion of said shank extending a predetermined distance along the axis of movement and movable with the shank, biasing means holding the shank in a nominal return position, a first coil wound about said shank to permit its axial movement through the coil and extending in the region of said magnetic material to substantially the terminal end of the magnetic material at the end of the shank remote from the key button, a second coil wound about the 2. Structure as'd'efined in claim 1 wherein a hood of low reluctance magnetic material surrounds said coils, said plate and said shank to provide a low reluctance return path for magnetic flux extending from said remote end of said magnetic material-in the shank. I

3. Structure as-d'efined in claim 1 including a source of continuous pulses coupled to said first coil, means coupled to said second coil for receiving a plurality of pulses from said source whenever the shank is moved' from said return position, and means convening said plurality of -pulses to a single output pulse. comprising a hysteresis circuit responsive to two selected threshold valves encountered intermediate in a range of amplitudes of pulses from said source encountered as the magnetic material of said shank enters the second coil during shank movement to produce only one output response pulse axis of said shank to permit its axial movement through the coil and placed substantially adjacent said first coil beyond the terminal end of the magnetic material in said shank, and a magnetic plate of low reluctance material placed between the coils and closely enough surrounding said shank to establish a low reluctance flux path return from said remote end of the magnetic material when the magnetic material is confined within the first coil as the key button is in said return position, whereby said two coils are mutually magnetically coupled with a low reluctance path through the magnetic material of said shank only when the shank is moved enough to pass the end of for each shank reciprocation, said single output pulse being derived from said output response pulse.

4. Structure as defined in claim 3 wherein said hysteresis circuit comprises a flip-flop circuit, and structure integrating pulses from said source of pulses to set the flip-flop at one threshold level and to reset the flip-flop at a different threshold level from the integrated pulses. 5. Structure as defined in claim I having a source of pulses connected for transfer between said two coils when the mag netic material of said key shank is axially moved into a position encompassing both said coils, including hysteresis circuit means responsive to pulses transfered from said source at the coils to provide a single indication of a reciprocation cycle of said shank including means integrating said pulses and means detecting two different threshold levels of the integrated pulses to define therebetween a hysteresis band where variations of pulse amplitude due to variations of coupling between said coils are made ineficctive. 

1. Structure operable in an electronic keyboard comprising in combination, an electronic key device manually actuable from a key button having a longitudinally oriented shank coupled to the key button and movable axially over a confined span of longitudinal movement, magnetic material of low reluctance in at least a portion of said shank extending a predetermined distance along the axis of movement and movable with the shank, biasing means holding the shank in a nominal return position, a first coil wound about said shank to permit its axial movement through the coil and extending in the region of said magnetic material to substantially the terminal end of the magnetic material at the end of the shank remote from the key button, a second coil wound about the axis of said shank to permit its axial movement through the coil and placed substantially adjacent said first coil beyond the terminal end of the magnetic material in said shank, and a magnetic plate of low reluctance material placed between the coils and closely enough surrounding said shank to establish a low reluctance flux path return from said remote end of the magnetic material when the magnetic material is confined within the first coil as the key button is in said return position, whereby said two coils are mutually magnetically coupled with a low reluctance path through the magnetic material of said shank only when the shank is moved enough to pass the end of the magnetic material in the shank through said magnetic plate to enter the second coil.
 2. Structure as defined in claim 1 wherein a hood of low reluctance magnetic material surrounds said coils, said plate and said shank to provide a low reluctance return path for magnetic flux extending from said remote end of said magnetic material in the shank.
 3. Structure as defined iN claim 1 including a source of continuous pulses coupled to said first coil, means coupled to said second coil for receiving a plurality of pulses from said source whenever the shank is moved from said return position, and means converting said plurality of pulses to a single output pulse comprising a hysteresis circuit responsive to two selected threshold valves encountered intermediate in a range of amplitudes of pulses from said source encountered as the magnetic material of said shank enters the second coil during shank movement to produce only one output response pulse for each shank reciprocation, said single output pulse being derived from said output response pulse.
 4. Structure as defined in claim 3 wherein said hysteresis circuit comprises a flip-flop circuit, and structure integrating pulses from said source of pulses to set the flip-flop at one threshold level and to reset the flip-flop at a different threshold level from the integrated pulses.
 5. Structure as defined in claim 1 having a source of pulses connected for transfer between said two coils when the magnetic material of said key shank is axially moved into a position encompassing both said coils, including hysteresis circuit means responsive to pulses transfered from said source at the coils to provide a single indication of a reciprocation cycle of said shank including means integrating said pulses and means detecting two different threshold levels of the integrated pulses to define therebetween a hysteresis band where variations of pulse amplitude due to variations of coupling between said coils are made ineffective. 